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# Gas Mark

The Gas Mark is a system and unit of marking temperatures on gas ovens and cookers in the United Kingdom and Commonwealth of Nations countries. It is still in use; however, it is not as widespread as it was in the last half of the twentieth century.

The draft 2003 edition of the Oxford English Dictionary lists the earliest known usage of the concept as being in L. Chatterton's book Modern Cookery published in 1943: "Afternoon tea scones… Time: 20 minutes. Temperature: Gas, Regulo Mark 7". This particular example also illustrates the term in combination with the word "regulo". This usage pattern is now almost obsolete, but still used by some of the older members of society.

The term "gas mark" was a subject of the joint BBC / OED TV series Balderdash & Piffle, in May 2005, which sought to establish the history of the term.

The earliest printed evidence of use of "gas mark" (with no other terms between the two words) appears to date from 1958.[1]

Conversion table
Gas mark Fahrenheit Celsius Verbal
14225°107°Very Slow/Very Low
12250°121°Very Slow/Very Low
1 275°135°Slow/Low
2 300°149°Slow/Low
3 325°163°Moderately Slow/Warm
4 350°177°Moderate/Medium
5 375°191°Moderate/Moderately Hot
6 400°204°Moderately Hot
7 425°218°Hot
8 450°232°Hot/Very Hot
9 475°246°Very Hot

Different manufacturers and oven types do vary, so always refer to your cooker instruction book.

In general, the conversions between a Gas Mark temperature TG and a Fahrenheit temperature TF are given by[citation needed]

$T_F = \begin{cases} 25 \log_2(T_G) + k_f & \mbox{if }T_G \le 1\\ 25 (T_G-1)+k_f & \mbox{if }T_G\ge 1\end{cases}$

and

$T_G = \begin{cases} 2^{\frac{T_F-k_f}{25}} & \mbox{if }T_F \le k_f \\ \frac{T_F-k_f}{25}+1&\mbox{if }T_F\ge k_f \end{cases}$

where the Fahrenheit constant kf takes the value kf = 275.